[hcraig244]

I’m pretty sure the dust cover is meant to close under the spring tension, mine does and I think its normal operation…..lifting the lid manually and the spring closes it ;¬)

Craig

[hcraig244]

Are you sure its not the 21vdc that is fed from PCB2 ?

I have had a problem with the voltage regulator for the 21vdc in  the past

Craig

[hcraig244]

Making a start on “the low hanging fruit”, to quote a project manager I once worked with. A friend of mine spent some time cleaning up the curser.  Interestingly this piece isn’t anodised like the face plate, which is probably why it oxidised so badly, I’m told that one can determine if something has been anodised by the use of a multimeter set to ohms……if something is anodised it wont conduct?….I will test this. New felt pads will be included too.

[hcraig244]

Sold as fully functional…….however I think a bit of cleaning (quite a bit actually) and replacing of dried out capacitors will be required before power is connected, some replacement veneer too I’m thinking

[hcraig244]

Its in a bit of a state…..looks like its been through the wars

[hcraig244]

So ready to be returned to its home……been quite a journey, the success is largely due to Manfys inspiration and guidance  regarding the voltage regulator and toroidal transformer.

Its good to know that a failed transformer isn’t the end of the road for a BG4000

[hcraig244]

Played over the weekend without fault………

[hcraig244]

Installed the voltage regulator, bolted to the chassis, no additional heatsink required….gave her a spin and nothing is getting more than lukewarm….Martin recommends removing 2TR6 from the circuit board due to overheating causing the 6vdc supply to become unstable…..so I’m good with this, good test required and that should be that!

[hcraig244]

Resistor received, however I ordered a 3w component and received a 25w instead……bit overkill but quite adequate….

[hcraig244]

As I’m now down to 1 bridge rectifier I thought it would be wise to check a few things out before I do a lengthy test run:

Output from the new 6vdc regulator = 160ma under operating load

Output from the existing 24vdc regulator (0tr1) = 440ma under operating load

The transformer arms are good for 1.25A so I think we’re good to go, the bridge rectifier is rated at 3.7A. I will monitor the temperatures of all components, TR1 particularly though the data sheet says its good for 80w (seems high to me).

Also I have ordered a 33 ohm 3w resistor to see if I can drop all the heat over it instead of the regulator, I can then fasten the resistor to the chassis for cooling……

[hcraig244]

Tried a 22 ohm resistor in line with the regulator and this dropped the input voltage to a little over 10vdc…the heat dissipated by the regulator has dropped and the resistor is doing some of the work….

[hcraig244]

This is the current wiring detail I have implemented……..

[hcraig244]

this is the input to the new voltage regulator from the centre tap of the the transformer, much improved though still a little high, this measurement was taken under load, this was previously sitting at 24v

 

[hcraig244]

moving on…..got the dual outputs from the centre tapped transformer sorted out, after a good deal of head scratching….and glasses of wine! I removed the 6vdc bridge rectifier and reinstalled the smoothing capacitor, output from the centre tap connection of the transformer to the input of the new regulator and now get a decent full wave rectification.

cant seem to get a jpeg loaded……..maybe later

[hcraig244]

This looks like an issue with the centre tapped transformer, I have read on the internet that a common neutral on the DC outputs of dual supplies of different voltages fed from centre tapped transformers are not allowed, this may be my problem.

When I disconnect the 24vac supply from the transformer to the 24vdc rectifier I get the expected 12vdc from the output of the 12vdc rectifier, so I know the 12vdc rectifier is working fine..I have no problems with the 24vdc side which is working fine, as this is the required higher supply im not surprised.  I cant see anything untoward except the common neutral to both rectifiers……..any advice regarding this would be welcome, as always ;¬)

[hcraig244]

Ok…..cleaned the drawing up to include the actual transformer wiring details and took some measurements…..these are all with the turntable running and under normal load conditions…everything works fine though the voltage regulator gets hot…put a heat sink on it which helps quite a bit.

[hcraig244]

This is how the new power supply is tied in…

[hcraig244]

However the 6vdc fell off when the regulator went into high temp cut off……it was getting very hot!….few measurements revealed that I am getting 24v at the input to the voltage regulator instead of the 12v i was expecting, the output from the transformer is 12v to the 6v rectifier…..

[hcraig244]

This is the regulator 6vdc output under operating load

[hcraig244]

This is how it looks, I have the regulator connected on leads to allow measurments to be taken easily

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